1. Technical Field
The present invention relates to a transmitting device and a transmitting method, particularly to a transmitting device and a transmitting method, which conduct FSK-modulated wireless communication with a receiving device.
2. Related Art
A fob key (FOB) that is used in a keyless entry system of a vehicle transmits a command signal such as lock/unlock to a vehicle-side ECU when a user pushes a push button switch such as lock/unlock of the FOB. The vehicle-side ECU actually performs the lock/unlock of a vehicle door when the command signal is authenticated as a signal transmitted from the previously-registered FOB.
Because communication between the FOB and the vehicle-side ECU is wirelessly conducted, sometimes the communication is interrupted by turbulence or the like (noise). It is conceivable that increasing output intensity of the signal in order to prevent the communication interruption caused by the turbulence or the like. However, in the keyless entry system, an upper limit of the output intensity of the wireless communication used by the FOB is stipulated by a law, and the signal cannot be transmitted at the output intensity exceeding the upper limit. Therefore, in order to prevent the interruption caused by the turbulence or the like, there is well known a method, in which a frequency of the signal transmitted from the FOB to the vehicle-side ECU is changed to conduct communication at a frequency at which the turbulence or the like has a little influence.
For example, Japanese Unexamined Patent Publication No. 2008-101344 discloses a vehicle control system that securely conducts communication in the keyless entry system. In the vehicle control system of Japanese Unexamined Patent Publication No. 2008-101344, a smart fob key (FOB) transmits a keyless wireless signal for the keyless entry system in two frequency channels. On the other hand, an integrated tuner that receives the keyless wireless signal determines the frequency channel having a better communication state in the two frequency channels, and controls the keyless wireless signal of the determined frequency channel so as to convert the keyless wireless signal into an intermediate frequency signal. As a result, the keyless wireless signal of the frequency channel having the better communication state is received to securely conduct communication.
In the vehicle control system of Japanese Unexamined Patent Publication No. 2008-101344, it is necessary to use a plurality of frequency channels, and it is necessary to provide a circuit that transmits and receives the plural frequencies in not only the transmitting device side (FOB) but also the receiving device (vehicle-side ECU).